Polycrystalline silicon and Al (aluminum) have been used mainly in the past as electrode and wiring materials of semiconductor integrated circuits formed on a Si (silicon) substrate. As semiconductor devices have been scaled down in recent years, however, attempts have been made to introduce refractory metals such as W (tungsten), Ti (titanium), cobalt, etc, and their silicide compounds, as new electrode and wiring materials because these metals and metal compounds have lower resistance than Si and higher electromigration resistance than Al.
The refractory metal (silicide) film for these electrode and wiring materials is formed on a semiconductor wafer by sputtering in argon a target that is prepared by sintering powder of the refractory metal (silicide).
Japanese Patent Laid-Open Nos. 192974/1994, 192979/1994 and 3486/1995 disclose a technology for producing high purity Co which reduces its impurity contents, particularly the Ni (nickel) and Fe (iron) contents, and has a purity of over 99.999% (5N), by an electrolytic refining process. This high purity Co is applied to the production of a Co target for forming a Co film used for the electrodes and wiring lines (electrodes, gates, wiring lines, devices, protective films, etc.) of semiconductor devices.
Japanese Patent Laid-Open No. 1370/1993 describes a method of producing a refractory metal silicide target for sputtering, capable of restricting the formation of particles that would otherwise result in breakage and short-circuit of the electrodes and wiring lines. This reference illustrates W, Mo (molybdenum), Ta (tantalum), Ti, Co and Cr (chromium) as the refractory metals.
The refractory metal silicide film can be formed by a refractory metal film to react with silicon, besides the method described above that uses the target of the refractory metal silicide.
Japanese Patent Laid-Open No. 321069/1995 describes a so-called “Salicide process” which comprises the steps of forming a Co-Ti film on the entire surface of a semiconductor substrate, on which MOSFETs (Metal Oxide Semiconductor Field Effect transistors) are formed, by a magnetron sputtering process using a composite metal target constituted by 20 atom % of a ferromagnetic material such as Co and 80 atom % of a paramagnetic material such as Ti, then conducting heat-treatment so as to form a Co silicide-Ti silicide mixture layer on the polycrystalline silicon gates as well as on the sources and drains, removing unreacted potions of the mixture layer by etching, and conducting again the heat-treatment to thereby reduce the resistance of the mixture layer.